Each year hundreds of millions of dental restorations are performed, and an ever-increasing fraction of these restorations involve the use of photopolymerizable polymer composites. Unfortunately, these composites suffer from significant problems that limit their applicability and utility. The primary issue limiting their applicability and utility is associated with the polymerization shrinkage and shrinkage induced stressesthat arise during the polymerization. This shrinkage results from the conversion of the reactive methacrylate double bonds into single bonds and results in numerous problems including microleakage, mechanical failure, and secondary caries. Other significant issues also exist with polymer composite restorations including the long timeframe for polymerization, lack of toughness of the resin material, moisture uptake by the polymer network following polymerization, the presence of extractable, unreacted monomer following cure, and inhibition of the polymerization by oxygen. The result of these problems is often the premature failure of composite restorations. In this research we hope to address each of these critical shortcomings by (i) developing novel monomer systems that will be more rapidly polymerizable, reach higher double bond conversions, improve the mechanical properties, and limit the effects of oxygen inhibition, (ii) synthesizing and utilizing novel functional groups that form reversible crosslinks and enable dramatic, true stress relaxation during photopolymerization, and (iii) developing a comprehensive understanding of the critical stress evolution and potential elimination that facilitates the application of the first two aims in a system which exhibits near-quantitative reduction in the polymerization stress. These aims are predicated on the hypothesis that appropriate materials synthesis and design coupled with optimization of polymerizations conditions will lead to enhanced polymeric dental composites with respect to shrinkage stress, polymerization speed (or reduction in the initiator content), moisture uptake and reduced extractablesand improved biocompatibility. Results to date have already demonstrated an extremely rapid polymerization, lower volume shrinkage and stress, near elimination of oxygen inhibition, and an ability to eliminate nearly all stress by radical generating reactions in crosslinked films. These results will combine to yield dramatically improved dental composite systems with enhanced longevity and improved clinical scope.